1. Field of the Invention
This invention relates generally to leak detection systems that employ a liquid or other fluid permeable leak detection cable to determine the occurrence and location of a leak in an area being monitored.
2. Description of the Prior Art
Various leak detection systems are known. Among such system are time domain reflectometry (TDR) systems such as, for example, the system disclosed in U.S. Pat. No. 4,797,621, incorporated herein by reference. In such time domain reflectometry systems, a pulse is sent down a transmission line and the reflected pulses are monitored. A change in the time of arrival or the shape of a reflected pulse indicates a leak and the location of the leak along the cable. Other systems utilize resistive cables whose resistance is measured and provides an indication of the location of a leak. Examples of such a systems are illustrated in U.S. Pat. Nos. 4,926,165 and 5,015,958. While the above-identified systems provide a way to detect and locate leaks, neither system can differentiate between non-conductive and conductive leaks.
In an attempt to distinguish between conductive and non-conductive leaks, systems utilizing separate cables and separate monitoring stations monitoring each of the cables have been installed. In such a system a cable that allows only hydrocarbons to penetrate is used in conjunction with a cable that allows both hydrocarbons and water to penetrate in a time domain reflectometry system. The TDR system can then be used to determine whether a leak is conductive or non-conductive based on whether one or both cables have been penetrated.
While these systems do provide a way to detect leaks and in some cases differentiate between conductive and non-conductive leaks, these system are relatively complicated and in many instances only have limited range.